ESP8266 Community Forum

Would I need some level converters if I want to connect http://arduino.cc/en/Main/USBSerial to esp8266 RX and TX?
I mean are 8266 rx and tx 5V tolerant or I need to use voltage level shifters?
I am trying to design 220V enabled esp8266, with SSR relay and some sensors.

No, can't use that one. You need to find one that can do 3.3V, as the ESP8266 is not 5V tolerant. Sparkfun has some, Adafruit too. If you want to order on ebay, make sure you have one that can do 5V/3.3V with a switch. Otherwise you might fry the chip.

Pete

make sure you have one that can do 5V/3.3V with a switch.

Hmm... I've just found this video:
https://www.youtube.com/watch?v=ZeA_mJalXFg
So, beware of USB to serial adapters, even those with a switch. At 4:19, that video shows a handy trick to know the output level: Connect Tx to Rx and measure the voltage between that and ground.
http://youtu.be/ZeA_mJalXFg?t=4m19s
As a side note, I'm using the cheapest adapter I could find on eBay, and it outputs 3.36V, measured with that trick and a multimeter, and also with an oscilloscope during a firmware upload. It's based on the Prolific PL2303HX chip.

Lot of people mentionned that a simple resistor voltage divider was working fine for them.
(Personnaly, my USB adaptor has 3V output)